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DOS (MS-DOS, PC-DOS, etc.)
The very first operating system used on the earliest IBM PCs was called simply the Disk
Operating System, abbreviated DOS. There are few PC users who have not heard
of DOS; at one time it was used on pretty much every PC, and it is still around today in
many different forms. Microsoft's version of DOS is the most common one, and is called
MS-DOS--with the "MS" abbreviation being rather self-explanatory. :^) For a
while IBM Corporation was producing a competing product called PC-DOS, and there are other
companies' alternatives around as well.
As the name "DOS" implies, the use of disks is an inherent part of the DOS
operating system. The FAT file system has been an essential
component of DOS since the beginning, and generally speaking, DOS uses only various
versions of FAT for managing files. Different flavors of FAT (sorry :^) ) are supported by
different versions of DOS, as follows:
- DOS 1.x and 2.x: These ancient DOS versions support only the FAT12 file
system, used today primarily for floppy disks. If you're still using DOS 1.x or 2.x, man
do you need a new computer! :^)
- DOS 3.x through 6.x: These are more common versions of DOS for older
PCs running either straight DOS or Windows 3.x. DOS 6.x was
especially popular; millions of copies of these operating systems were sold. DOS 3.x
through 6.x support the older FAT12 and the newer FAT16, which was the file system
standard for many years in the PC world.
- DOS 7.0: MS-DOS 6.22 was the last "standalone" version of DOS
sold by Microsoft. After DOS6.22, Microsoft sold DOS only as the underpinnings of other
operating systems, such as Windows 95/98/ME. The first of these was MS-DOS 7.0, which runs
"underneath" the first Windows 95 version (Windows 95A). It supports FAT12,
FAT16 and VFAT, the enhanced version of FAT that includes support for long file names.
- DOS 7.1 and later: These versions of DOS underlie Windows versions from
Windows 95 OEM Service Release 2 (Windows 95B) and later. They support FAT12, FAT16, VFAT
and FAT32.
The most confusion is caused by the "appearance" of FAT32 support in the
second release of Windows 95--corresponding to DOS 7.1--which was complicated by the fact
that later versions of Windows that support FAT32 were not "officially" sold to
the public. See the discussions of Windows 95A and Windows 95B and 95C for more information.
 Tip: You can check the
version of DOS your system is running by using the "VER" command from any DOS
command line. Note that this may not work for DOS running under a Windows version, as
Microsoft desperately wants people to think that Windows 95/98/ME do not run on the
ancient DOS platform. ;^)
 Next: Windows 3.x
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